1. Field of the Invention
The present invention relates to electrical contactors and similar devices for completing and interrupting electrical current-carrying paths between a source and a load. More particularly, the invention relates to a coil assembly and actuator for such a device which facilitates assembly and installation, and which provides improved electrical and magnetic performance during energization deenergization phases of operation.
2. Description of the Related Art
A great variety of devices have been designed for completing and interrupting current-carrying paths between an electrical source and an electrical load. In one type of device, commonly referred to as a contactor, a set of movable contacts is displaced relative to a set of stationary contacts, so as to selectively complete a conductive path between the stationary contacts. In remote-controllable contactors of this type, an actuating assembly is provided to cause the movable contacts to shift between their open and closed positions. Such actuating assemblies typically include a coil forming an electromagnet, and a core to intensify a magnetic field generated around the coil when an actuating current is passed therethrough. The magnetic field attracts a movable armature which is coupled to the movable contacts within the device, thereby displacing the movable contacts and thus making electrical contact or closing the electrical circuit. When the actuating current is removed, biasing members return the movable assembly back to its normal position thus breaking the electrical connection or opening the electrical circuit.
Contactors of the type described above are commonly available with either alternating current or direct current actuating coil assemblies. The selection of either an alternating current assembly or a direct current assembly typically depends upon the type of electrical power available in the application. However, advantages and disadvantages are associated with each type of assembly. For example, direct current coils can be associated with simple solid core structures which do not need laminations to minimize heating from circulating eddy currents found in alternating current coils. Also, direct current coils tend to have a higher force to power ratio because the current is steady and does not pass through zero with each half cycle as is the case with alternating current, and therefore require lower currents to obtain a desired armature pull-in or contact retaining force. Moreover, direct current assemblies do not require shading coils as are typically provided in alternating current assemblies, and therefore are quieter in operation and experience lower wear. On the other hand, alternating current power sources are very widespread and are favored in many cases due to their availability.
Coil assemblies for contactors have also been constructed with multiple coils, including coaxially aligned pickup coils and holding coils. Because a Greater coil MMF is required to close the contactor than is required during steady-state operation, both the pickup and holding coils may be energized during an initial closure period, with the pickup coil being deeneregized following the closure period. The pickup coil is designed to have a significantly higher MMF and power than the hold coil. Turning off the pickup coil minimized heating and reduces the power required once the armature has closed (i.e. steady state operation). Timing for deenergization of the pickup coil is typically fixed, and is set so as to provid e sufficient force and time for displacement of the movable contact assembly to a closed position. However, if the time, force or power supply varies, as is sometimes the case, such arrangements may either provide insufficient or excessive periods of energization of the pickup coil.
There is a need, therefore, for an improved actuating technique for contactors and similar electrical devices. In particular, there is a need for an actuating coil assembly which can be powered by either AC or DC power, while providing sufficient transient response capabilities, particularly during release of a holding coil. Moreover, there is a need for an operator assembly and control method wherein a DC coil can be quickly removed from a circuit upon deenergization, and which permits rapid release of a movable armature without the production of an opposing magnetic field under the influence of induced currents.